1 /*
   2  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  14  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  15  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  16  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  17  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  18  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  19  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  20  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  22  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  23  */
  24 
  25 #include "includes.h"
  26 RCSID("$OpenBSD: kexdh.c,v 1.18 2002/03/18 17:50:31 provos Exp $");
  27 
  28 #pragma ident   "%Z%%M% %I%     %E% SMI"
  29 
  30 #include <openssl/crypto.h>
  31 #include <openssl/bn.h>
  32 
  33 #include "xmalloc.h"
  34 #include "buffer.h"
  35 #include "bufaux.h"
  36 #include "key.h"
  37 #include "kex.h"
  38 #include "log.h"
  39 #include "packet.h"
  40 #include "dh.h"
  41 #include "ssh2.h"
  42 
  43 void
  44 kexdh_server(Kex *kex)
  45 {
  46         BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
  47         DH *dh;
  48         Key *server_host_key;
  49         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  50         u_int sbloblen, klen, kout;
  51         u_int slen;
  52 
  53         /* generate server DH public key */
  54         dh = dh_new_group1();
  55         dh_gen_key(dh, kex->we_need * 8);
  56 
  57         debug("expecting SSH2_MSG_KEXDH_INIT");
  58         packet_read_expect(SSH2_MSG_KEXDH_INIT);
  59 
  60         if (kex->load_host_key == NULL)
  61                 fatal("Cannot load hostkey");
  62         server_host_key = kex->load_host_key(kex->hostkey_type);
  63         if (server_host_key == NULL)
  64                 fatal("Unsupported hostkey type %d", kex->hostkey_type);
  65 
  66         /* key, cert */
  67         if ((dh_client_pub = BN_new()) == NULL)
  68                 fatal("dh_client_pub == NULL");
  69         packet_get_bignum2(dh_client_pub);
  70         packet_check_eom();
  71 
  72 #ifdef DEBUG_KEXDH
  73         fprintf(stderr, "dh_client_pub= ");
  74         BN_print_fp(stderr, dh_client_pub);
  75         fprintf(stderr, "\n");
  76         debug("bits %d", BN_num_bits(dh_client_pub));
  77 #endif
  78 
  79 #ifdef DEBUG_KEXDH
  80         DHparams_print_fp(stderr, dh);
  81         fprintf(stderr, "pub= ");
  82         BN_print_fp(stderr, dh->pub_key);
  83         fprintf(stderr, "\n");
  84 #endif
  85         if (!dh_pub_is_valid(dh, dh_client_pub))
  86                 packet_disconnect("bad client public DH value");
  87 
  88         klen = DH_size(dh);
  89         kbuf = xmalloc(klen);
  90         kout = DH_compute_key(kbuf, dh_client_pub, dh);
  91 #ifdef DEBUG_KEXDH
  92         dump_digest("shared secret", kbuf, kout);
  93 #endif
  94         if ((shared_secret = BN_new()) == NULL)
  95                 fatal("kexdh_server: BN_new failed");
  96         BN_bin2bn(kbuf, kout, shared_secret);
  97         memset(kbuf, 0, klen);
  98         xfree(kbuf);
  99 
 100         key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
 101 
 102         /* calc H */
 103         hash = kex_dh_hash(
 104             kex->client_version_string,
 105             kex->server_version_string,
 106             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 107             buffer_ptr(&kex->my), buffer_len(&kex->my),
 108             server_host_key_blob, sbloblen,
 109             dh_client_pub,
 110             dh->pub_key,
 111             shared_secret
 112         );
 113         BN_clear_free(dh_client_pub);
 114 
 115         /* save session id := H */
 116         /* XXX hashlen depends on KEX */
 117         if (kex->session_id == NULL) {
 118                 kex->session_id_len = 20;
 119                 kex->session_id = xmalloc(kex->session_id_len);
 120                 memcpy(kex->session_id, hash, kex->session_id_len);
 121         }
 122 
 123         /* sign H */
 124         /* XXX hashlen depends on KEX */
 125         key_sign(server_host_key, &signature, &slen, hash, 20);
 126 
 127         /* destroy_sensitive_data(); */
 128 
 129         /* send server hostkey, DH pubkey 'f' and singed H */
 130         packet_start(SSH2_MSG_KEXDH_REPLY);
 131         packet_put_string(server_host_key_blob, sbloblen);
 132         packet_put_bignum2(dh->pub_key);     /* f */
 133         packet_put_string(signature, slen);
 134         packet_send();
 135 
 136         xfree(signature);
 137         xfree(server_host_key_blob);
 138         /* have keys, free DH */
 139         DH_free(dh);
 140 
 141         kex_derive_keys(kex, hash, shared_secret);
 142         BN_clear_free(shared_secret);
 143         kex_finish(kex);
 144 }